This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-034233, filed Feb. 12, 1999; and No. 11-079636, filed Mar. 24, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a rolling device, particularly to a rolling device using a lubricant.
In general, in a rolling device such as a ball-and-roller bearing or a rectilinear device, abrasion of the rolling body and the member in contact with the rolling body is prevented by circulating or sealing a lubricant such as a lubricating oil like a mineral oil or poly-xcex1-olefin oil or a grease within the rolling device.
Such a rolling device can be used under the ordinary use conditions without giving rise to a problem. However, where the rolling device is driven under, for example, a high temperature, high speed or vacuum condition, the lubricant is scattered to the outside of the rolling device, or the lubricant is evaporated to generate a gas. As a result, the outer environment of the rolling device is contaminated. For that reason, a fluorine-based grease is used in many cases as a lubricant of the rolling device in an apparatus used in a clean room such as a semiconductor manufacturing apparatus, a liquid crystal panel manufacturing equipment and a hard disk manufacturing equipment; a vacuum equipment in which the rolling device is exposed to a vacuum condition such as a vacuum pump; and the equipment used under high temperatures.
The fluorine-based grease is a mixture of a liquid fluorinated polymer oil as a base oil and a solid fluorinated polymer as a thickener. In general, the fluorine-based grease is very low in its volatility, and the amount of the grease scattered to the outside of the rolling device or evaporated is very small. It follows that the outer environment of the rolling device is relatively unlikely to be contaminated.
However, the liquid fluorinated polymer contained in the fluorine-based grease has in general a high viscosity, leading to a difficulty, particularly where the rolling device using the fluorine-based grease as a lubricant is driven at a high speed. Specifically, since the lubricant has a large resistance to stirring, the torque is rendered excessively high so as to increase the heat generation. As a result, in the case of the ball-and-roller bearing, the inner ring, the outer ring, and the rolling body are expanded. It follows that the clearance between the adjacent members is diminished so as to make the load excessively large at the contact surfaces between the inner ring and the rolling body and between the outer ring and the rolling body. As a result, an abnormal abrasion and seizing are brought about so as to render the rolling device unusable in a short time. Naturally, the rolling device must be renewed frequently.
Also, in recent years, the evacuation capacity and the evacuation rate tend to be increased in the vacuum pump. To be more specific, the rotating speed of the rolling device used in the vacuum pump is sharply increased nowadays. Therefore, the heat generation is increased so as to bring about the abnormal abrasion and seizing as described above. As a result, the rolling device is rendered unusable in a short time and the vacuum pump is rendered inoperable in a short time.
As described above, where a fluorine-base grease is used as a lubricant of a rolling device operated under a high temperature, high speed or vacuum condition, an abnormal abrasion and seizing tend to be derived from the high viscosity of the fluorine-based grease. Naturally, it is desirable for the rolling device used under a high temperature, high speed or vacuum condition to be driven without inviting contamination of the outer environment and an increased torque.
The problem described above takes place not only under a high temperature, high speed or vacuum condition but also under a low temperature condition. When it comes to a rolling device used in, for example, an equipment for cooling or freezing an electronic element, the temperature elevation is derived from the resistance to stirring accompanying the driving of the rolling device. As a result, where a mineral oil, poly-xcex1-olefin oil or the like is used as the lubricant of the rolling device, the outer environment of the rolling device, e.g., the coolant used for the cooling or freezing, is contaminated. Thus, the cooled element such as the electronic element is contaminated with the lubricant component. Also, since, in this case, the evaporation and disappearance of the lubricant are promoted by the coolant, a sufficient lubricity ceases to be obtained by the use for a short time. Under the circumstances, the fluorine-based grease was widely used in the past as a lubricant of the rolling device under the condition requiring a low temperature and a clean environment as in the refrigerator and freezer.
However, the ordinary fluorine-based grease has a high viscosity, as already pointed out. Particularly, the fluorine-based grease has a very high viscosity under a low temperature condition, giving rise to an increase in the resistance to stirring, i.e., an increase in the torque of the rolling device. As a result, it is impossible to drive the rolling device in some cases. Also, even if the rolling device can be driven, an excessively large load is applied to the motor for driving the rolling device. In addition, the heat generation accompanying the driving of the motor is rendered excessively large so as to evaporate the lubricant and, thus, to contaminate the coolant.
It should also be noted that some of the fluorine-based greases has a high vapor pressure. Where such a fluorine-base grease is used as a lubricant of the rolling device used under the low temperature condition, the evaporation caused by the heat generation noted above is rendered more prominent. In this case, the evaporation and disappearance of the lubricant are promoted by the coolant, as pointed out above, with the result that a sufficient lubricity ceases to be obtained in a very short time.
In accordance with miniaturization of the design rule of the electronic element in recent years, demands for preventing contamination tend to become severer and severer against the cooling and freezing equipment of the electronic element. Also, in accordance with miniaturization and energy saving of the cooling and freezing devices, the torque of the rolling device constituting a part of the driving section tends to be decreased so as to suppress the loss of the power and to prolong the life of the driving section, thereby achieving a mechanism free from maintenance.
However, the lubricant used in the conventional rolling device gives rise to an increase in the torque and to contamination of the cooled member. In addition, the lubricant gives rise to the problem that a sufficient lubricity ceases to be obtained in a short time. Under the circumstances, it is desirable for the rolling device used under low temperature conditions to be driven without giving rise to contamination of the outer environment and to an increase in the torque.
The problem derived from the lubricant is generated not only in the case where the rolling device is used in the apparatus described above. In other words, the problem derived from the lubricant is also generated in the case where the rolling device is used for the other purposes, as described below.
As widely known to the art, a ball-and-roller bearing using grease as a lubricant is utilized in general in the electrical components of an automobile, an alternator that is an auxiliary member of an engine, an intermediate pulley, an electromagnetic clutch for an automotive air conditioner, etc.
Diminishment of an engine room is required for the automobile in accordance with popularization of a front-wheel-drive vehicle intended to miniaturize and decrease the weight of the automobile and with requirement for an enlarged cabin. Such being the situation, vigorous efforts are being made in an attempt to miniaturize and decrease the weight of the electrical components, the auxiliary members of the engine, etc. However, it is unavoidable for the miniaturization to be accompanied by reduction of output. Therefore, the reduction in the output is compensated by driving, for example, the alternator or the electromagnetic clutch for the automotive air conditioner at a higher speed. Naturally, the intermediate pulley is also driven at a high speed.
It is also required that the quietness of the automobile be increased. To meet this requirement, the sealing of the engine room is being promoted. However, the sealing of the engine room, which is certainly effective for improving the quietness, promote the temperature elevation within the engine room. It follows that the various parts within the engine room are required to exhibit a higher resistance to heat.
Nowadays, a grease prepared by adding a urea compound as a thickener to a base oil of a synthetic oil is used as a lubricant of a ball-and-roller bearing in the above-noted parts used in the field described above. The urea-synthetic oil series grease exhibits a sufficiently long lubricant life of the bearing under temperatures up to about 170xc2x0 C. to 180xc2x0 C. Therefore, if the temperature of the ball-and-roller bearing is elevated to only about 170xc2x0 C. to 180xc2x0 C., the particular grease can be used sufficiently as a lubricant of the ball-and-roller bearing.
However, the rolling bearing tends to be exposed to higher temperatures in recent years. For example, in a certain alternator, the cooling water of a radiator is used for the cooling inside the alternator, with the result that the bearing temperature exceeds 200xc2x0 C. in some cases. Where the above-noted urea-synthetic oil series grease is used as a lubricant in a ball-and-roller bearing whose temperature is increased to about 200xc2x0 C., the grease is hardened by evaporation of the base oil. In some cases, the thickener is broken so as to soften the grease. As a result, a problem is generated that the seizing is generated in an early stage.
An object of the present invention is to provide a rolling device adapted for use under a severe condition such as a high temperature, a high operating speed, a vacuum and a low temperature conditions and exhibiting an excellent torque life even if driven under such a severe condition.
Another object is to provide a rolling device adapted for use under a severe condition such as a high temperature, a high operating speed, a vacuum and a low temperature conditions, capable of suppressing contamination of the outer environment, and exhibiting an excellent torque life, even if driven under such a severe condition.
Further, still another object of the present invention is to provide a rolling device exhibiting a sufficient resistance to seizing even under the condition of a high temperature, a high operating speed, and a heavy load.
According to a first aspect of the present invention, there is provided a rolling device comprising a movable member capable of a rotary movement or a linear movement, a support member supporting the movable member, a rolling body interposed between the movable member and the support member and rolled in accordance with the movement of the movable member, and a lubricant arranged between the movable member and the support member on which the rolling body is rolled, wherein the lubricant is a grease composition containing a mixture of base oil and a thickener, the base oil being a liquid fluorinated polymer oil having a kinetic viscosity at 40xc2x0 C. of 10 mm2/sec to 400 mm2/sec.
According to a second aspect of the present invention, there is provided a rolling device comprising a movable member capable of a rotary movement or a linear movement, a support member supporting the movable member, a rolling body interposed between the movable member and the support member and rolled in accordance with the movement of the movable member, and a lubricant arranged between the movable member and the support member on which the rolling body is rolled, wherein the lubricant contains as a base oil either one of (1) a liquid fluorinated polymer oil having a kinetic viscosity at xe2x88x9220xc2x0 C. falling within a range of between 100 mm2/sec and 3,000 mm2/sec, and a vapor pressure at 50xc2x0 C. of 2xc3x9710xe2x88x924 Torr or less, and (2) a liquid fluorinated polymer oil having a kinetic viscosity at 40xc2x0 C. of 10 mm2/sec to 400 mm2/sec and a kinetic viscosity at 100xc2x0 C. of 3 mm2/sec to 80 mm2/sec.
In the rolling device of the present invention, a predetermined liquid fluorinated polymer oil is used as a base oil of the lubricant, with the result that rolling device can be used satisfactorily even under severe conditions.
For example, in the rolling device of the present invention, the lubricant containing as a base oil a liquid fluorinated polymer oil having a kinetic viscosity at xe2x88x9220xc2x0 C. of 100 mm2/sec to 3,000 mm2/sec and having a vapor pressure at 50xc2x0 C. of 2xc3x9710xe2x88x924 Torr or less is adapted for use under low temperature conditions.
Where the rolling device of the present invention is used under these conditions, it is desirable for the liquid fluorinated polymer oil to exhibit a kinetic viscosity at xe2x88x9220xc2x0 C. falling within a range of between 100 mm2/sec and 2500 mm2/sec and to exhibit a vapor pressure at 50xc2x0 C. of 5xc3x9710xe2x88x925 Torr or less. It is more desirable for the liquid fluorinated polymer oil to exhibit a kinetic viscosity at xe2x88x9220xc2x0 C. falling within a range of between 100 mm2/sec and 2000 mm2/sec and to exhibit a vapor pressure at 50xc2x0 C. of 2xc3x9710xe2x88x925 Torr or less.
The rolling device of the present invention, the lubricant of which contains as a base oil a liquid fluorinated polymer oil exhibiting a kinetic viscosity at 40xc2x0 C. of 10 mm2/sec to 400 mm2/sec and a kinetic viscosity at 100xc2x0 C. of 3 mm2/sec to 80 mm2/sec, is adapted for use under a high temperature, high operating speed or vacuum condition.
Where the rolling device of the present invention is used under such a condition, it is desirable for the liquid fluorinated polymer oil to exhibit a kinetic viscosity at 40xc2x0 C. of 13 mm2/sec to 320 mm2/sec and to exhibit a kinetic viscosity at 100xc2x0 C. of 4 mm2/sec to 60 mm2/sec. It is more desirable for the liquid fluorinated polymer oil to exhibit a kinetic viscosity at 40xc2x0 C. of 15 mm2/sec to 270 mm2/sec and to exhibit a kinetic viscosity at 100xc2x0 C. of 5 mm2/sec to 50 mm2/sec.
Also, where the rolling device of the present invention is used under a high temperature, high operating speed or vacuum condition, it is desirable for the lubricant to contain an oily compound having a perfluoropolyether skeleton as a backbone chain, with a polar group at one end or both ends of the backbone chain, and having a molecular weight not higher than 10,000. It is desirable for the oily compound to be contained in the lubricant in an amount of 0.5 to 10% by weight.
The rolling device of the present invention, in which the lubricant is a grease composition containing a mixture of a base oil and a thickener and the base oil is a liquid fluorinated polymer oil having a kinetic viscosity at 40xc2x0 C. of 10 mm2/sec to 400 mm2/sec, is adapted for use under high temperature, high operating speed and heavy load condition.
Where the rolling device of the present invention is used under the condition, it is desirable for the liquid fluorinated polymer oil to exhibit a kinetic viscosity at 40xc2x0 C. of 13 mm2/sec to 320 mm2/sec. It is more desirable for the liquid fluorinated polymer oil to exhibit a kinetic viscosity at 40xc2x0 C. of 15 mm2/sec to 270 mm2/sec.
In the rolling device of the present invention, it is desirable for the lubricant to contain as a thickener at least one material selected from the group consisting of a solid fluorinated polymer, a layered mineral powder, an ultra fine particle and a white powder substantially all the components thereof being nonmetal elements.
Where the lubricant contains a thickener defined above, it is desirable for the thickener to be contained in an amount of 10 to 45% by weight, preferably 15 to 40% by weight, and more preferably 20 to 35% by weight, based on the total amount of the lubricant.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.